The present invention relates to a sizing tool for sizing the outer dimensions of an extruded tubing.
The sleeve-like sizing tools of said type are placed immediately after a tubing extruder, in a specific sizing and cooling vat.
The operation of the tools complies with two principles. According to one principle, a tubing in a forming state and leaving the extruder is pressed against the inner surface of the sizing tool by means of pressure developed inside the tubing. The other operating principle requires a work chamber under vacuum, in which chamber the sizing tool is placed. The wall of the tool is provided with through channels, via which the vacuum prevailing in the work chamber can affect the outer surface of the tubing in the sizing tool. The tubing is then sucked against the inner surface of the tool.
For cooling the tubing, the tool is either immersed in water acting as a coolant medium or the tool is subjected to a constant water shower.
From the point of view of a satisfactory operation of sizing tools, it is essential that the tubing passes through the tool as free from friction as possible and that the tubing leaving the extruder is correctly cooled for achieving the desired dimensions and dimensional stability.
For achieving these objects, different lubricating and cooling solutions have been developed for sizing tools. These solutions related to sizing tools operating both under an internal pressure and an external vacuum have been described in patent literature to a great extent.
The sizing tool according to this invention can be adapted to be used both in pressure and vacuum systems. When it is used in a vacuum system, the wall of the sizing tool must be provided with pressure passages.
A sizing tool provided with pressure passages and a channel system communicating with the inner surface of the tool for leading lubricating water essentially along the whole tool length between the outer surface of the tubing and the inner surface of the tool is known and described e.g. in the U.S. Pat. No. 4,543,051.
In the sizing tool described in said reference publication, the cooling is mainly based on the effect of cooling water in the sizing vat, although the lubricating water naturally participates in the cooling. However, arranging the cooling and the lubrication in said manner limits the tool capacity, nor does it provide a possibility of adjusting the cooling without a detrimental effect on the lubrication.